Management of biological and chemical constituents for the advancement of intensive, minimal-exchange, biofloc-based shrimp (Litopenaeus vannamei) aquaculture

Andrew James Ray

Abstract

Intensive, minimal-exchange, biofloc-based shrimp aquaculture systems may provide a sustainable alternative to traditional shrimp culture. Through a series of experiments, this document explores the effects of several key management strategies on water quality, isotopic distribution, and shrimp production. An experiment evaluated the effects of managing suspended solids (biofloc) concentration at two levels. It was found that using a higher flow rate to larger settling chambers resulted in significantly lower biofloc and nitrate concentrations, and significantly improved shrimp growth rate. A second experiment compared systems with clear water and systems with biofloc. The filters in the clear water systems prevented biofloc accumulation and cycled nutrients, whereas biofloc systems occasionally contained dangerous concentrations of ammonia and nitrite. Using stable isotope analysis it was estimated that biofloc contributed 72% of the carbon and 42% of the nitrogen found in shrimp from those tanks. A third study was conducted exploring carbohydrate addition as a means of stimulating bacterial nitrogen assimilation. Without carbohydrate addition nitrification proceeded, exemplified by a nitrite spike and an accumulation of nitrate, with carbohydrate addition those compounds were in low concentration. Shrimp production was poor in the treatment receiving molasses, but similar among the treatment without carbohydrate, and treatments with glycerol and sucrose additions. In a fourth experiment three salinities were evaluated: 10, 20, and 30[per thousand]. The pH was lower as salinity increased and nitrite was significantly higher in the 30 versus the 10[per thousand] salinity treatments. Mean shrimp growth rate was 1.9 g wk -1 and the mean feed conversion ratio was 1.3:1; these parameters did not differ significantly between treatments. Lastly, an experiment was conducted to evaluate the utilization of biofloc by juvenile shrimp in a nursery phase. Data suggested that both feed and biofloc contributed carbon to shrimp. A two-source isotope mixing model indicated that between 34 to 50% of the nitrogen in shrimp came from the biofloc. The results of these studies can help biofloc shrimp culture managers decide how to operate systems. The improved success and continued development of such systems may provide the shrimp aquaculture industry a viable option for ecologically responsible development and intensification.